An operating system is a large, complex piece of software whose primary function is the management of hardware and software resources of a data processing system such as processors, memory and storage. Storage management, in turn, involves the organization of storage devices, such as disks, into logical groupings to achieve various performance and availability characteristics. For example, the disks may be arranged to create individual volumes or concatenations of volumes, mirror sets or stripes of mirror sets, or even redundant arrays of independent disks (RAID). The data processing platform on which the operating system executes to provide such management functions typically includes a host computer coupled to a storage adapter or controller. The operating system functionally organizes this platform by, inter alia, invoking input/output (I/O) operations in support of software processes or applications executing on the computer.
A storage architecture of the operating system decomposes management of the storage devices into individual components and defines their functional operations with respect to the flow of information and control among them. The individual components include an I/O subsystem and a file system, each of which is generally independent of one another and interact according to interfaces defined by the architecture. The I/O subsystem provides an efficient mode of communication between the computer and the disks that allows programs and data to be entered into the memory of the computer for processing; the subsystem also enables the results obtained from computations of that information to be recorded on the disks.
The file system contains general knowledge of the organization of information on the storage devices and provides algorithms that implement properties of the desired storage architecture. To that end, the file system is a high-level software entity comprising a collection of program modules, e.g., software drivers, that incorporate a command set for the storage devices/disks. Typically, the operating system implements a file system to logically organize the information as a hierarchical structure of files on the disks.
I/O processing is typically performed under the auspices of the file system in that applications typically interact with the file system to manipulate (i.e., read or write) the files. I/O subsystems, on the other hand, interact with disks at lower software levels by manipulating blocks of data. Accordingly, a single I/O transaction operation requested by an application to the file system may spawn into many I/O transfer operations between the I/O subsystem and disks; that is, there may be multiple data transfers between the lower-layer software entities and the actual hardware devices.
Some storage architectures provide their file systems and I/O subsystems entirely on the controller of the data processing platform. Here, the host computer interacts with the controller in accordance with a conventional client-server computing model wherein the host computer ("client") forwards each I/O transaction request to the controller ("server") typically across an interconnection such as a network. Architectures implementing the client-server model are typically referred to as loosely-coupled or distributed system architectures because computations are distributed among several computing elements, each with its own processor and memory. In contrast, tightly-coupled systems are characterized by computing elements that share communication resources, such as an interface or bus.
An example of a server-specific I/O architecture that is optimized for file operations of a Unix file server is described in U.S. Pat. No. 5,163,131 titled Parallel I/O Network File Server Architecture by Edward J. Row et al, issued on Nov. 10, 1992. Row discloses a file server architecture that comprises one or more network controllers, one or more file controllers, one or more storage processors, and a memory interconnected by a message passing bus and operating in parallel with the Unix host. Client requests for file operations are transmitted to a file controller which, independently of the Unix host, manages a virtual file system of a mass storage device coupled to the storage processors.
Although the architecture described in Row relieves the host processor from I/O processing, it also adversely affects file system latency, i.e., the period of time between the issuance of an I/O transaction request by an application to the file system and the completion of that request by the file system. In general, file system latency increases with an architecture having a file system that is remote from the processing platform on which the application executes.
Therefore, it is an object of the present invention to provide a storage architecture communication interface of a data processing system that increases overall file system performance.